Experimental and analytical study on properties affecting the behaviour of FRP-confined concrete

In this study the results of a large test program are presented with the objective of examining the effect of various experimental parameters on the confinement effectiveness of FRP jackets on both circular and rectangular concrete columns with solid or hollow core. The experimental parameters include: different concrete strength, type of fibres, number ofwrap layers, geometry of the column, corners radius, full/hollow core and cross-sectional aspect ratio (only for prismatic elements). FRP-confined and unconfined specimens have been loaded in uniaxial compression until failure. Totally 128 specimens were prepared and tested, 89 of them were strengthened with Carbon FRP (CFRP) and Glass FRP (GFRP), the remaining 39 were tested as plain concrete reference. Compressive stress, axial and hoop strains have been measured to evaluate the stress–strain relationships, ultimate strength, stiffness, and ductility of the specimens. Results confirmed that external confinement produced by FRP can significantly enhance compressive strength, ductility and energy absorption capacity if compared to those of plain concrete. The effects of test parameters are evidenced and compared in order to show the sensitiveness of the mechanical problem for each of them. Important design information are furnished to researchers and practitioners also by comparing the results of the experimental campaign with the prediction of different analytical models, based on well-known and widely accepted mechanical assumptions. Design equation recommended by CNR (Italian National Research Council) were also applied by assuming unitary values for safety factors, in order to see the reliability of the mechanical model proposed by CN

FRP-Confinement of Hollow-Core Concrete Cylinders and Prisms

The use of hollow-core reinforced concrete (RC) sections for bridge piers has become a popular engineering practice to obtain a reduction of the self-weight (especially in seismic zones) and a better structural efficiency in terms of the strength/mass and stiffness/mass ratios. In contrast to this popularity in practice, scientific studies on the mechanical behavior of such structural elements are limited. The use of Fiber Reinforced Polymer (FRP) materials for external confinement of hollow core columns and piers is an almost unknown field at the moment. The research work presented herein aims at evaluating the influence of various experimental parameters on the effectiveness of FRP jackets applied to hollow concrete columns. Hollow-core concrete prisms and cylinders were tested under uniaxial compression to study the stress-strain relationship before and after FRP jacketing. A range of experimental parameters were investigated: different concrete strength, type of fibers, number of wrap layers, column shape and dimensions, and for square and rectangular sections, the corner radius and the cross-sectional aspect ratio. Axial strain was measured by LVDTs, while strains in the fibers were recorded by electrical strain gauges. Circular columns wrapped with FRP showed a significant increase in terms of both strength and ultimate displacements. Results obtained by laboratory tests were close to those recorded for FRP-confined concrete, which means that the increase in ultimate load was found to be comparable to that found in full circular sections. Rectangular columns showed a lower increase in ultimate capacity, compared to circular sections, even if the results related to ultimate axial displacement encourage adopting this technique for seismic retrofit to fulfill higher ductility requirements in both prismatic and cylindrical columns

FRP-Confinement of Concrete Cylinders and Prisms

The use of fibre reinforced polymer (FRP) composites has been successfully promoted for external confinement of reinforced concrete (RC) columns and pillars all over the world. Increase in compressive capacity and energy absorption before collapse have been largely experienced in laboratory environment during the last decade, especially by testing concrete cylinders wrapped with FRP jackets. In this study the results of a large test program are presented with the objective of examining the effect of various experimental parameters on the confinement effectiveness of FRP jackets on both circular and rectangular concrete columns. The experimental parameters include: different concrete strength, type of fibres, number of wrap layers, geometry of column, corners radius and cross-sectional aspect ratio for rectangular columns. FRP-confined and unconfined specimens have been loaded in uniaxial compression. Compressive stress, axial and hoop strains have been measured to evaluate the stress-strain relationships, ultimate strength, stiffness, and ductility of the specimens. Results confirmed that external confinement produced by FRP can significantly enhance strength, ductility and energy absorption capacity if compared to those of plain concrete. The effects of test parameters are evidenced and compared; important design information is furnished to researchers and practitioners

Stress strain relationship of FRP-confined concrete for hollow columns

Past studies demonstrated the structural efficiency of FRP-confinement for reinforced concrete (RC) columns to increase their strength and ductility in axial compression [1-4]. Numerical and analytical models were developed to predict the stress-strain behavior of FRP confined concrete [5-8] and recommendations were provided to practitioners for design of FRP-retrofitted RC columns. Scientific studies related to FRP-confinement of hollow-core RC columns are very limited at the moment; a few data reporting properties of RC hollow-core columns under seismic forces are available [9-11]. This clashes with the thousands of applications all over the world in which bridge piers are designed as hollow-core columns to maximize the structural efficiency in terms of strength/mass and stiffness/mass ratios. In this work both solid and hollow-core concrete prisms and cylinders were tested under uniaxial compression to study the influence of various experimental parameters on the effectiveness of FRP jackets applied to concrete columns subjected to uniaxial compression loading. The investigated parameters were the concrete strength, the fibers type, the number of wrap layers, the column shape and dimensions and, for prismatic sections, the corner radius and the cross-sectional aspect ratio. On the basis of the experimental results obtained, a nonlinear finite element model was developed, obtaining a good correlation between the experimental and the numerical data in terms of stress-strain curves and ultimate load

Interaction of substituted poly(phenyleneethynylene)s with ligand-stabilized CdS nanoparticles

The interfacial region of surface-modified semiconducting nanoparticles and polymers contributes to the limited efficiency of hybrid photovoltaic cells and has been analyzed by molecular simulation at atomic resolution to complement experimental measurements.</p